Distributed Debugging and Monitoring on $5 a Day

One of the principal impediments to debugging and monitoring distributed systems is the diiculty of implementing the required infrastructure. If remote de-bugging and monitoring were universally available at low cost and with minimal implementation eeort it might lead to increases in the integrity and robustness of distributed systems. We describe a technique that brings universal distributed debugging and monitoring within easy grasp. The fundamental observation is that the Hypertext Transport Protocol (HTTP), the enabling protocol of the World Wide Web (WWW), is just a general-purpose synchronous Remote Procedure Call (RPC) with the ability to carry arbitrary arguments and results. Consequently, by embedding a small web server in the runtime environment of any programminglanguage, it is possible to implement, using standard HTTP and Hypertext Markup Language (HTML), the medium of expression of Web pages, powerful remote debugging and monitoring facilities that can be accessed by anyone equipped with an In-ternet connection and a web browser. This paper describes Joist, an embedded web server developed for just this purpose, its architecture, and its use in implementing a remote debugging and monitoring environment for a complex wireless device.